This invention relates to a motion simulator and is more particularly concerned with improvements in motion simulators comprising a deck supported by a number of length adjustable legs.
For simulating motions, in particular vehicle motion such as for instance of aircraft, boats, trains and automobiles, motion simulators are used comprising a deck that is arranged on a number of movable legs. The deck can be moved within a motion envelope through a change of the lengths of the legs. Such motion simulator is known as a Stewart Platform and is discussed in Stewart, D., A Platform with six-degrees-of-freedom", in Proc.Inst. of Mechanical Engineers, Vol. 180, Part 1, No. 5, 1965-1966, pp. 371-386, herein incorporated by reference.
The deck of this known motion simulator is a flat plate stiffened by means of a load-bearing beam construction. Via the beam construction, the legs are attached to the bottom side of the plate by means of first pivot points, while on the top side of the deck a simulation environment is built up. In this manner, during the motions of the deck the legs are prevented from being obstructed by any element of the part of the simulator supported by the legs. The simulation environment comprises for instance a cockpit of an aircraft or other vehicle reproduced on the deck, while outside the reproduced cockpit, on the deck, means are provided for presenting a simulated environment. Furthermore, inter alia an instructors cabin, control and information means and conditioning means for the atmosphere in the simulator, as well as a casing which surrounds the part of the simulator that is supported by the legs can be positioned on the deck.
Since the deck is a flat, beam-stiffened plate construction, the advantage is achieved that the deck is relatively inexpensive, whereas almost any simulation environment can be reproduced. However, this known simulator has the drawback that the deck with the simulation environment built thereon may be heavy and has specific stiffnesses only to a limited extent. An increase of the stiffnesses results in an even higher mass of the construction,
Since the moving part of the simulator is heavy, a high load-bearing capacity of at least the legs is necessary. Consequently the response time of the simulator, that is the delay time between the provision of a control signal and the reaction of the simulator thereto becomes unacceptably high, the more so since the high weight of the simulator represents a great inertia. These high response times, which are typically at 100 milliseconds and more, cause the simulated behaviour of the vehicle to becomes unnatural, in particular in the case of simulation of vehicles that in reality have very short response time, such as for instance vehicles on wheels, aircrafts and the like. This response time lag results in a less effective simulation. Moreover, the operator can be adversely influenced, for instance through the occurrence of motion sickness. In principle, these high response times can at least partly be compensated through anticipation, but this is only possible for vehicle and environment characteristic input signals, not for signals inputted by the operator. Moreover, this is complicated from the view point of control engineering and hence costly. A high weight of the moving part of the simulator further has an adverse effect on the natural frequency and damping of the motion simulator and on the influence of interference signals, and, moreover, the part can be accelerated only to a limited extent.
A further drawback of a motion simulator of the known type is that it is not optimized for the simulation of the desired vehicle or working environment. The envelope of movement of the deck differs strongly from the necessary space for accurately simulating the specific movements of the vehicle or working environment. This results in acceleration and deceleration of considerably more mass than necessary, whereas a relatively large space is necessary for such motion simulator. Furthermore, this known motion simulator has the disadvantage that in at least a number of directions of movement undesired limits of movement will be reached for at least a number of the supporting legs, constituting singularities and resulting in difficult, it not impossible control of the movements of the deck and a negative influence on the accuracy, of the simulation. There above, the distribution of forces to and by the legs is not optimal, disadvantageously influencing the construction and the possible accelerations and decelerations of the leg supported part and the forces necessary thereto.